(a) Technical Field
The present invention relates to a system and method for diagnosing failure of a thermostat, and more particularly, to a system and method for diagnosing failure of a thermostat which senses failure of a thermostat opening function due to an increase in temperature of a coolant by the influence of an exhaust gas recirculation (EGR) cooler before an engine warms up.
(b) Background Art
Thermostats are devices disposed between a water pump and a radiator in a vehicle and maintain a constant engine temperature by opening or closing a valve based on the temperature of a coolant. The thermostats circulate a coolant to radiators by contracting and closing a valve when the coolant temperature decreases to a predetermined threshold and by thermally expanding and opening the valve when the coolant increases in temperature, using a material such as wax or pellet which contracts and expands with a change in temperature.
However, when the thermostats are open (hereafter, referred to as an ‘open status’) and fixed, a coolant keeps flowing to the radiator, and particularly, at the early stage of cold start, and the timing of an engine warm-up delays and combustion stability and catalyst activation deteriorate. As a measure against this problem, failure in the open status of the thermostats needs to be diagnosed.
FIG. 1 is an exemplary view schematically showing the flow of a coolant in a structure equipped with an EGR system. Referring to FIG. 1, with an EGR system applied, when temperature of a coolant rapidly increases due to the influence of a coolant that exchanged heat via an EGR cooler 2, a thermostat 3 opens and cools an engine 1 before the engine is warmed up, thereby delaying the timing of the engine warm-up.
However, even though the thermostat 3 opens early before the engine 1 warms up, the existing systems for diagnosing failure may not recognize the problem, but may recognize it as a normal open status of the thermostat. In addition, even in this type of system, it may be difficult to accurately diagnose the problem of opening of a thermostat before an engine warms up due to the influence of an EGR cooler.
The description provided above as a related art of the present invention is just for helping understanding the background of the present invention and should not be construed as being included in the related art known by those skilled in the art.